This class merges solver.xsd and benchmark.xsd into a single XML Schema file that contains both Solver and Benchmark XML
types under a single namespace of the benchmark.xsd.
Both solver.xsd and benchmark.xsd declare its own namespace as they are supposed to be used for different purposes. As the
benchmark configuration contains solver configuration, the benchmark.xsd imports the solver.xsd. To avoid distributing
dependent schemas and using prefixes in users' XML configuration files, the types defined by solver.xsd are merged to
the benchmark.xsd under its namespace.